Trump named McMaster his national security adviser last month. The Senate had roughly two months to reconfirm him to his three-star rank, or he would automatically drop down to a two-star.

There is precedent for an active-duty military member to serve as national security adviser.

Colin Powell was a lieutenant general when he was appointed national security adviser in 1987 and retained his rank after a Senate vote.

But then-Sen. Sam Nunn (D-Ga.) had some concerns about whether active-duty military should serve in the White House.

Nunn noted that while he would support Powell, he took a "dim view" of other active-duty members serving in the position.

"Any active-duty officer who serves in that position may be subject to an inherent conflict between his responsibilities to the president and his own professional future in the service," he said in a 1987 floor speech.